The human spinal column is prone to diseases or disorders that produce disruption of the normal alignment of the spine. Frequently, treatment of spinal disorders involves spinal stabilization, for example, by immobilization of the affected vertebral joint(s). One spinal stabilization technique includes a surgical process wherein implants are attached to the spinal vertebrae and connected with spinal rods. In particular, a combination of bone screw arrangements and connecting rods are used to provide a stabilizing construct secured to the spinal vertebrae for the purpose of stabilizing and/or adjusting spinal alignment.
FIG. 1 illustrates one conventional bone screw arrangement 1 for use with a connecting rod 7. The arrangement 1 includes an anchor 2, a yoke member 3, and an internal locking piece 4. The internal locking piece 4 has an outer tapered surface, and is positioned within a correspondingly tapered bore 5 of the yoke member 3.
In use, the connecting rod 7 is aligned with the yoke member 3 for placement of the connecting rod within the saddle of the yoke member 3. Because connecting rods are often times bent to correspond to the curvature of the patent's spinal structure, positioning the connecting rod within the saddle of the yoke member can be difficult.
Once the connecting rod 7 is properly positioned, a lock nut 6 is tightened down onto the yoke member 3. The lock nut 6 forces the connecting rod 7 into the saddle of the yoke member 3 and against the top of the locking piece 4, while at the same time, drawing the yoke member 3 upwardly relative to the locking piece 4 (see relative motion represented by arrows in the enlarged detail view). As the lock nut 6 draws the yoke member 3 upward, and forces the connecting rod 7 downward, the tapered arrangement of the yoke member 3 and the internal locking piece 4 causes the locking piece 4 to compress radially inward. Compression of the locking piece 4 causes the locking piece 4 to clamp on the head of the anchor 2 to fix the anchor 2 at a desired angular orientation relative to the yoke member 3. Concurrently, the rod 7 is clamped between the nut 6 and the top of the locking piece 4.
As can be understood, the size of a bone screw arrangement is an important aspect in minimizing the invasiveness of a surgical stabilization procedure. In the arrangement of FIG. 1, at least three components: the anchor 2, the yoke member 3, and the locking piece 4, functionally dictate the size of the arrangement.
In general, improvement has been sought with respect to such devices and arrangements, generally to better accommodate: manufacture and assembly, ease of use, reduced invasiveness, and, adaptability for a variety of spinal surgery applications.